[论文解读] The rise and fall of the Type Ib supernova iPTF13bvn - Not a massive Wolf-Rayet star

C. Fremling, J. Sollerman+10 more|arXiv (Cornell University)|Mar 26, 2014

Gamma-ray bursts and supernovae参考文献 36被引用 46

一句话总结

本研究利用广泛的测光和光谱数据重新评估了Ia型超新星iPTF13bvn的前身星，否定了此前提出的单颗大质量沃尔夫-拉叶星前身星模型。对总光光 light curve 的流体动力学建模揭示出较低的抛射物质量（1.9 M⊙）和较低的⁵⁶Ni质量（0.05 M⊙），这与大质量WR前身星不一致，表明更可能是质量较小的双星系统。

ABSTRACT

We investigate iPTF13bvn, a core-collapse (CC) supernova (SN) in the nearby spiral galaxy NGC 5806. This object was discovered by the intermediate Palomar Transient Factory very soon after the explosion and was classified as a stripped-envelope CC SN, likely of Type Ib. A possible progenitor detection in pre-explosion Hubble Space Telescope (HST) images was reported, making this the only SN Ib with such an identification. Based on photometry of the progenitor candidate and on early-time SN data, it was argued that the progenitor candidate is consistent with a single, massive Wolf-Rayet (WR) star. In this work we present follow-up multi-band light-curves and optical spectra of iPTF13bvn. We perform spectral line analysis to track the evolution of the SN ejecta, construct a bolometric light curve and perform hydrodynamical calculations to model this light curve to constrain the synthesized radioactive nickel mass and the total ejecta mass of the SN. Late-time photometry is analyzed to constrain the amount of oxygen. Furthermore, image registration of pre- and post-explosion HST images is performed. Our HST astrometry confirms the location of the progenitor candidate, and follow-up spectra securely classify iPTF13bvn as a SN Ib. Our hydrodynamical model indicates an ejecta mass of 1.9 solar masses and radioactive nickel mass of 0.05 solar masses. The model fit requires the nickel to be highly mixed out in the ejecta. The late-time nebular r'-band luminosity is not consistent with predictions based on the expected oxygen nucleosynthesis in very massive stars. Our bolometric light curve of iPTF13bvn is not consistent with the previously proposed single massive WR-star progenitor scenario. The ejecta mass and the late-time oxygen emission are both significantly lower than what would be expected from a single WR progenitor with a main-sequence mass of at least 30 solar masses.

研究动机与目标

• 确认预爆发哈勃空间望远镜（HST）图像中iPTF13bvn前身星的检测结果。
• 通过额外的光学光谱对iPTF13bvn进行稳健分类。
• 检验iPTF13bvn的观测测光和光谱演化是否与单颗大质量沃尔夫-拉叶星前身星一致。
• 通过总光光曲线的流体动力学建模约束抛射物质量和⁵⁶Ni质量。
• 评估晚期电离态光度测量与大质量恒星核合成预期的氧生成的一致性。

提出的方法

• 在预爆发和爆发后HST图像之间执行图像配准，以确认前身星候选体的天体测量位置。
• 从多波段测光（UBVRI, g′r′i′z′）构建覆盖早期至晚期阶段的总光光曲线。
• 应用Arnett（1982）的半解析模型和Cano（2013）的方法论来解释总光光曲线。
• 使用流体动力学代码HYDE对光曲线进行建模，并约束总抛射物质量和⁵⁶Ni质量。
• 分析晚期电离态r′波段测光以推断氧质量，与大质量恒星核合成预测进行比较。
• 对后续光学光谱进行标准谱线分析，以追踪抛射物速度演化并确认Ib型超新星分类。

实验结果

研究问题

• RQ1 在预爆发HST图像中识别出的前身星候选体是否真正与iPTF13bvn的爆发位置相关联？
• RQ2 iPTF13bvn的测光和光谱演化是否支持其前身星为单颗大质量沃尔夫-拉叶星？
• RQ3 通过总光光曲线的流体动力学建模，推断出的抛射物质量和⁵⁶Ni质量分别是多少？
• RQ4 观测到的晚期电离态光度是否与初始质量≥30 M⊙的前身星预期的氧生成一致？
• RQ5 iPTF13bvn的观测特性能否由单星演化模型解释，还是双星相互作用情景更为合理？

主要发现

• HST天体测量确认前身星候选体位于爆发位置，位置偏移小于80 mas。
• 后续光谱分析将iPTF13bvn可靠地分类为Ib型超新星，光球层速度与典型Ib型超新星一致。
• 总光光曲线的流体动力学建模得出总抛射物质量为1.9 M⊙，⁵⁶Ni质量为0.05 M⊙。
• 模型要求⁵⁶Ni在抛射物中高度混合，以重现观测到的光曲线，表明存在非对称混合。
• 晚期电离态r′波段光度与大质量恒星（≥30 M⊙初始质量）核合成预测的氧生成不一致。
• 较低的抛射物质量和较低的氧发射量排除了单颗大质量沃尔夫-拉叶星前身星，支持质量较小的双星系统。